cmd/geth, core/state/snapshot: fix flaw in dangling-storage check + inspect difflayers (#24677)

This PR fixes the flaw that @rjl493456442 found in https://github.com/ethereum/go-ethereum/pull/#issuecomment-1093817551 , namely, that the snapshot iterator uses the combined (disk + difflayers) 'view', wheres the raw iterator uses only the disk 'view'.

This PR instead splits up the work: one phase is iterating the disk layer data, another phase is loading the journalled difflayers and performing the same check there.

cmd/geth/snapshot.go

@@ -263,8 +263,12 @@ func verifyState(ctx *cli.Context) error {
 		return err
 	}
 	log.Info("Verified the state", "root", root)
-	if err := checkDangling(chaindb, snaptree.Snapshot(root)); err != nil {
-		log.Error("Dangling snap storage check failed", "root", root, "err", err)
+	if err := checkDanglingDiskStorage(chaindb); err != nil {
+		log.Error("Dangling snap disk-storage check failed", "root", root, "err", err)
+		return err
+	}
+	if err := checkDanglingMemStorage(chaindb); err != nil {
+		log.Error("Dangling snap mem-storage check failed", "root", root, "err", err)
 		return err
 	}
 	return nil
@@ -277,33 +281,17 @@ func checkDanglingStorage(ctx *cli.Context) error {
 	defer stack.Close()
 
 	chaindb := utils.MakeChainDatabase(ctx, stack, true)
-	headBlock := rawdb.ReadHeadBlock(chaindb)
-	if headBlock == nil {
-		log.Error("Failed to load head block")
-		return errors.New("no head block")
-	}
-	snaptree, err := snapshot.New(chaindb, trie.NewDatabase(chaindb), 256, headBlock.Root(), false, false, false)
-	if err != nil {
-		log.Error("Failed to open snapshot tree", "err", err)
+	if err := checkDanglingDiskStorage(chaindb); err != nil {
 		return err
 	}
-	if ctx.NArg() > 1 {
-		log.Error("Too many arguments given")
-		return errors.New("too many arguments")
-	}
-	var root = headBlock.Root()
-	if ctx.NArg() == 1 {
-		root, err = parseRoot(ctx.Args()[0])
-		if err != nil {
-			log.Error("Failed to resolve state root", "err", err)
-			return err
-		}
-	}
-	return checkDangling(chaindb, snaptree.Snapshot(root))
+	return checkDanglingMemStorage(chaindb)
+
 }
 
-func checkDangling(chaindb ethdb.Database, snap snapshot.Snapshot) error {
-	log.Info("Checking dangling snapshot storage")
+// checkDanglingDiskStorage checks if there is any 'dangling' storage data in the
+// disk-backed snapshot layer.
+func checkDanglingDiskStorage(chaindb ethdb.Database) error {
+	log.Info("Checking dangling snapshot disk storage")
 	var (
 		lastReport = time.Now()
 		start      = time.Now()
@@ -323,17 +311,24 @@ func checkDangling(chaindb ethdb.Database, snap snapshot.Snapshot) error {
 			log.Info("Iterating snap storage", "at", fmt.Sprintf("%#x", accKey), "elapsed", common.PrettyDuration(time.Since(start)))
 			lastReport = time.Now()
 		}
-		data, err := snap.AccountRLP(common.BytesToHash(accKey))
-		if err != nil {
-			log.Error("Error loading snap storage data", "account", fmt.Sprintf("%#x", accKey), "err", err)
-			return err
-		}
-		if len(data) == 0 {
+		if data := rawdb.ReadAccountSnapshot(chaindb, common.BytesToHash(accKey)); len(data) == 0 {
 			log.Error("Dangling storage - missing account", "account", fmt.Sprintf("%#x", accKey), "storagekey", fmt.Sprintf("%#x", k))
 			return fmt.Errorf("dangling snapshot storage account %#x", accKey)
 		}
 	}
-	log.Info("Verified the snapshot storage", "root", snap.Root(), "time", common.PrettyDuration(time.Since(start)), "err", it.Error())
+	log.Info("Verified the snapshot disk storage", "time", common.PrettyDuration(time.Since(start)), "err", it.Error())
+	return nil
+}
+
+// checkDanglingMemStorage checks if there is any 'dangling' storage in the journalled
+// snapshot difflayers.
+func checkDanglingMemStorage(chaindb ethdb.Database) error {
+	start := time.Now()
+	log.Info("Checking dangling snapshot difflayer journalled storage")
+	if err := snapshot.CheckJournalStorage(chaindb); err != nil {
+		return err
+	}
+	log.Info("Verified the snapshot journalled storage", "time", common.PrettyDuration(time.Since(start)))
 	return nil
 }
 

core/state/snapshot/journal.go

@@ -345,3 +345,78 @@ func (dl *diffLayer) Journal(buffer *bytes.Buffer) (common.Hash, error) {
 	log.Debug("Journalled diff layer", "root", dl.root, "parent", dl.parent.Root())
 	return base, nil
 }
+
+// CheckJournalStorage performs consistency-checks on the journalled
+// difflayers.
+func CheckJournalStorage(db ethdb.KeyValueStore) error {
+	journal := rawdb.ReadSnapshotJournal(db)
+	if len(journal) == 0 {
+		log.Warn("Loaded snapshot journal", "diffs", "missing")
+		return nil
+	}
+	r := rlp.NewStream(bytes.NewReader(journal), 0)
+	// Firstly, resolve the first element as the journal version
+	version, err := r.Uint()
+	if err != nil {
+		log.Warn("Failed to resolve the journal version", "error", err)
+		return nil
+	}
+	if version != journalVersion {
+		log.Warn("Discarded the snapshot journal with wrong version", "required", journalVersion, "got", version)
+		return nil
+	}
+	// Secondly, resolve the disk layer root, ensure it's continuous
+	// with disk layer. Note now we can ensure it's the snapshot journal
+	// correct version, so we expect everything can be resolved properly.
+	var root common.Hash
+	if err := r.Decode(&root); err != nil {
+		return errors.New("missing disk layer root")
+	}
+	// The diff journal is not matched with disk, discard them.
+	// It can happen that Geth crashes without persisting the latest
+	// diff journal.
+	// Load all the snapshot diffs from the journal
+	return checkDanglingJournalStorage(r)
+}
+
+// loadDiffLayer reads the next sections of a snapshot journal, reconstructing a new
+// diff and verifying that it can be linked to the requested parent.
+func checkDanglingJournalStorage(r *rlp.Stream) error {
+	for {
+		// Read the next diff journal entry
+		var root common.Hash
+		if err := r.Decode(&root); err != nil {
+			// The first read may fail with EOF, marking the end of the journal
+			if err == io.EOF {
+				return nil
+			}
+			return fmt.Errorf("load diff root: %v", err)
+		}
+		var destructs []journalDestruct
+		if err := r.Decode(&destructs); err != nil {
+			return fmt.Errorf("load diff destructs: %v", err)
+		}
+		var accounts []journalAccount
+		if err := r.Decode(&accounts); err != nil {
+			return fmt.Errorf("load diff accounts: %v", err)
+		}
+		accountData := make(map[common.Hash][]byte)
+		for _, entry := range accounts {
+			if len(entry.Blob) > 0 { // RLP loses nil-ness, but `[]byte{}` is not a valid item, so reinterpret that
+				accountData[entry.Hash] = entry.Blob
+			} else {
+				accountData[entry.Hash] = nil
+			}
+		}
+		var storage []journalStorage
+		if err := r.Decode(&storage); err != nil {
+			return fmt.Errorf("load diff storage: %v", err)
+		}
+		for _, entry := range storage {
+			if _, ok := accountData[entry.Hash]; !ok {
+				log.Error("Dangling storage - missing account", "account", fmt.Sprintf("%#x", entry.Hash), "root", root)
+				return fmt.Errorf("dangling journal snapshot storage account %#x", entry.Hash)
+			}
+		}
+	}
+}